Electrical control apparatus



Jan. 7, 1941. T. A COHEN 2,228,163

ELECTRI CAL CONTROL APPARATUS Filed April 27, 1936 3 Sheets-Sheet 1 INVENTOR.

ATTORNEYS Jan. 7, 1941. A, COHEN 2,228,163

ELECTRI CAL CONTROL APPARATUS Filed April 27, 1936 3 Sheets-Sheet 2 INVENTOR.

K i g Jan. 7, 194-1. T. A. COHEN 3 8,

ELECTRICAL CONTROL APPARATUS Filed Apr-11 27, 1936 5 Sheets-Sheet 3 FIG-V INVENTOR.

"ayma'cww BY yaw, m *[JM ATTORNEYS 'Patented Jane 7, 1941 PATENT OFFICE ELECTRICAL CONTROL APPARATUS Theodore A. Cohen, Chicago, 111., assignor to Wheelco Instruments 00., Chicago, 111., a corporation oi Illinois Application April 27, 1936, Serial No. 76,708

23 Claims.

My invention relates to electrical control apparatus.

One of the objects .of my invention is to provide improved apparatus for enabling a vacuum tube oscillator to control a relay, which apparatus does not necessitate the engagement and disengagement of contacts for controlling the oscillator.

A further object of my invention is to provide such an apparatus which will be accurate and reliable in operation.

When a relay to be controlled by an oscillator circuit is directly connected for energization from the oscillator circuit itself, it is necessary to provide an extremely sensitive relay because of the small magnitude of the oscillator output current. Such sensitive relays require frequent and precise adjustment, and it is accordingly a further object of my invention to provide a control apparatus of the type indicated in which sensitive relays are eliminated and which provides a high degree of consistency of operation with a minimum amount of servicing.

Further objects and advantages of the invention will appear from the description and claims.

In the drawings, in which several embodiments of my invention are shown,

Figure 1 illustrates somewhat diagrammatically a control apparatus embodying my invenfm tion applied to the control of an electric furnace or the like;

Fig. 2 is a diagrammatic view showing another form of apparatus and circuit embodying my invention;

Fig. 3 shows still another form;

Fig. 4 is a fragmentary circuit diagram illustrating another arrangement of a sensitive instrument and thermo couple circuit for use in the control apparatus of Figs. 1, 2, and 5;

Fig. 5 is a circuit diagram illustrating what is now considered to be a preferred embodiment of my invention;

Fig. 6 is a plan view showing a preferred formof contactless control apparatus and sensitive inm strument means, such as a voltmeter, for use in connection with the circuits and apparatus shown in Figs. 1 to 5, inclusive; and

Fig. 7 is a side elevation of the apparatus shown in Fig. 6. v

In'the specific embodiments shown, the apparatus and circuits in general include an oscillator circuit having a load impedance in the output circuit, an amplifier or repeater tube controlled by the voltage drop across the load im- 60 pedance, a relay controlled by the output circult of the repeater or amplifier tube, and a contactless means for affecting the tuning of the oscillator circuit, thereby causing a charge in the current flowing through the load impedance to control the repeater tube and effect the oper- 5 ation of the relay. As is well known in this art, the plate current of an oscillator in oscillating condition is of a fixed value, depending upon plate voltage and grid bias. When the oscillator goes out of oscillation or oscillation changes 10 occur, the grid bias changes, causing a change in plate current. In the specific embodiment shown, I provide contactless apparatus comprising sensitive instrument means responsive to a condition to be controlled for affecting the os- 15 cillator circuit, thus causing a change in the oscillator plate current flowing through the load impedance, and take advantage of this current change for controlling the relay so as properly to control the condition to which the sensitive instrument means is responsive.

The apparatus and circuit of Fig. 1 comprises, as will be more fully described hereinafter, an oscillator circuit l which includes a tuning coil l3l, contactless sensitive instrument means 2 for affecting the oscillator circuit, and relay apparatus 3, controlled by the oscillator output change for controlling a condition to which the sensitive instrument means 2 is responsive. As shown in Fig. 1, the condition to be controlled is the temperature of an electric furnace 20, shown diagrammatically as including a heating circuit 2| connected through suitable contactors or other control apparatus 22 to a suitable source of energy represented by the supply conductors 23. The control apparatus 22, which may be of any suitable type well known'in the art, is connected through a plurality of control wires 24 to the contacts of the relay 3, whereby operation of the relay effects corresponding operation of the control apparatus 22 to control the heating circuit of the furnace 20. The sensitive instrument means 2, as shown best in Figs. 6 and 7, comprises a pointer or arm 4 mounted to swing about a pivot 5 and carrying a leaf orflag 8 of a metallic substance which, in the movement of the arm 4 about its pivot, swings between a pair of coils I and 8. In Fig. 1 the tuning coil II, which corresponds to the coils 1 and 8 of Figs. 6 and '7, is shown as a single coil, but it may obviously be formed in two parts corresponding to coils I and 8 of Figs. 6 and 7.

The-arm l, on which the. leaf or flag 8 is mounted, preferably carries an indicating pointer I5 cooperating with a scale l3 and may be part of any sensitive indicating system, such as a voltmeter or the like. The metallic leaf may be of any suitable shape or form and may be formed from any suitable metal or metals, de-

5 pending upon the characteristics desired.

In Fig. (1 the sensitive instrument means 2, the detailed construction of which will be more fully described in connection with Figs. 6 and '7, is shown as including an operating winding 30 10 connected through suitable conductors 3I to a thermo couple 32 located within the furnace 20 so as to be influenced by the temperature of the furnace. As will be apparent to those skilled in the art, fiuctuations'of the furnace temperature aifect the thermo couple 32 so as to vary the energization of the winding 30, whereby fluctuations in the furnace temperature are converted into corresponding movements of the arm 4 and the flag 6, movement of the flag B'being effective,

through the circuits shown in Fig. 1, to control the relay means 3, as will be hereinafter described, and thus control the heating circuit of the furnace.

Referring now to Figs. 6 and 7 which show one form of the sensitive instrument means 2 illustrated diagrammatically in Fig. 1, this sensitive instrument means, as shown, constituting a Darsonval type indicating movement, such as a voltmeter comprising a movable coil and 39 a pointer 4 pivotally mounted at 5, having an index finger "I5 cooperating with an arcuate scale I3 and carrying the flag 6 which cooperates with the coils 7 and 8 to affect the tuning of the 0scillator circuit. These coils I and 8 may be mounted on a setting lever I6 which may be pivotally mounted at 16a coaxially with the pointer 4 and which setting lever may also carry an index finger '5'! cooperating with the arcuate scale I3 and which setting lever I6 may be set 46 to any desired position by means of any suitable lever adjusting mechanism I8. As indicated above, when the flag 6 closely approaches the coils I and 8, an oscillator circuit will be affected, causing the operation of a relay. Such appara- 45 tus is useful in various situations, and in Fig. 1 is shown in connection with furnace temperature control, in which case the voltage controlling the position of the voltmeter pointer 4, as hereinbefore indicated, is produced by a thermo couple 50 so that when the voltage uCCEiSiOIlBd by the action of the thermo couple causes the flag to approach closely the coils I and 8, the relay will be operated to control the furnace temperature in any suitable manner.

55 Considering now the embodiment of the invention shown in Fig. l, the oscillator circuit, indicated generally by the reference numeral I, includes an electron discharge device or vacuum tube I34 having a control electrode or grid 40 6G and a pair of output electrodes comprising a cathode or filament 4i and an anode or plate 42. As shown, the input or grid circuit of the tube I 34 extends from the control electrode 40, through the conductor 43, the usual grid con- 55 denser 44 and grid-leak 45, and through the conductor 46 to the upper end of the tuning coil I 3I, the circuit being completed from the lower end of the coil I3I through a conductor 41 and a conductor 48 which is connected to the filament 70 or cathode 4!.

The output circuit of the tube I34, as shown, is supplied from a battery I37, although obviously other suitable energy sources may be used, and this output circuit may be traced from the 78 positive side of the battery through the conductor 43, a load impedance or resistor I33, 9. radio frequency choke coil III, a conductor 5|, a tank circuit including an inductance 52 and a variable condenser 53, and through the conductor 54 to the anode or plate 42. From the other side 5 of the battery the output circuit may be traced through the conductors 55 and 48 to the filament H and a by-pass circuit including conductors 56 and 51, and a by-pass condenser 53 is connected between the conductors El and 48,10 which by-pass circuit, in conjunction with the choke coil 50, prevents the flow of high frequency oscillatory currents through the load impedance I33 and the battery I 31, only the non-pulsating component of the plate current flowing through 15 the load impedance and the battery.

As will be apparent to those skilled in the art,

a fixed grid bias is applied to the control electrode 40 due to the grid leak and the grid condenser 44, and the above-described input cir- 2o cult of the tube I 34 constitutes a tuned circuit by reason of the distributed capacity of the tuning coil I3I. Thus, when the output or plate circuit of the tube I34 is tuned by adjustment of the condenser 53, so that the plate circuit is 25 in resonance with the grid or input circuit, the metal flag 6 being remote from the tuning coil I3I so that the coil is not affected thereby, sustained oscillations will be produced by the tube I34, the necessary feed-back coupling being pro- 30 vided by the interelectrode capacity of the tube and the by-pass condenser 58.

The vacuum tube constants of the oscillator I34 are so chosen that in the normal oscillating condition the non-pulsating component of the 3 plate current through the resistor I33 is low.

In order to effect operation of the relay 3 in response to changes in the plate current of the oscillator circuit I, a repeater or amplifier tube I32 is provided having an input electrode or grid 40 59, and output electrodes including a filament 60 and a plate 6i. As shown, the load impedance I33 is common to both the output circuit of the oscillator tube I 34 and the input circuit of the repeater tube I 32, the latter circuit extending 45 from the filament 60 through the conductors 62 and 63, the potentiometer I36 which is connected across a suitable bias battery 64, a conductor 65, the load impedance I33, and by way of a conductor 66 to the input electrode or grid 59. Normally with the oscillator tube I34 in oscillatory condition, the potentiometer I36 is adjusted so as to provide a voltage slightly less than the voltage drop across the load impedance I33, and accordingly a small negative bias is applied to the grid circuit of the tube I32, the voltage drop across the load impedance being due to the flow of normal low plate current in the oscillatory circuit.

The output circuit of the tube I32 is energized, as shown, from .a suitable battery I 38 and extends from the positive side of the battery through the conductor 61, the winding I35 of the relay 3, and by way of a conductor 68 to the plate SI. From the other side of the battery I38, this output circuit extends through conductors 69 and 62 to the filament 60. With a small negative bias on the grid 59, as indicated above, a relatively large current flows in the output circuit of the tube I32 and the winding I35 is accordingly en- 7 ergized so as to operate the movable contact of the relay 3 from the uppermost position shown in Fig. 1 into engagement with the lower stationary contact of the relay, engagement of these contacts being effective to energize a control cirours in the plate current of the tube I32.

cult including the conductors 24 so as properly to operate the furnace controlling contactors indicated diagrammatically at 22.

Upon the occurrence of a predetermined change in the temperature existing within the fumace' 20, the thermo couple 32 and the energizing winding III of the sensitive instrument means 2 are affected so as to move the arm 4 and cause the metal flag 6 to approach the tuning coil HI and effect a change in the tuning of the oscillator tube I34. Upon the vacuum tube oscillator I34 being aifected'by the approachment of the flag 3 to the coil I3I so as to disrupt the oscillatory condition, the plate current of the oscillator increases, causing a cdrresponding increase in the voltage drop across the load impedance I33 and a similar' increase in the nesative bias upon the vacuum tube I32. As a result of the increased negative bias on the input circuit thereof a consequent large decrease oc- This change in plate current correspondingly decreases the energization of the winding I35 of the relay 2 which controls the external contacting apparatus to the furnace 20, the movable contact of the relay 2 being released for movement to the uppermost position shown in Fig. 1. As indicated above, a. fixed grid bias for the vacuum tube I32 to prevent out off, due to the normal drop through the resistor I33 is derived from the potentiometer I33 and is of such value and nature as to allow the grid circuit of the tube I32 to be placed in the proper operating condition for efilcient relay action.

The construction shown in Fig. 2 is quite similar in most respects to that of Fig. 1 except that in Fig. 2 the apparatus is operated from an ordinary rectifled alternating current power supply I39, I40, the rectifier not being shown as it is well known in the art. These circuits may also be operated from unrectifled alternating current in a so-called self-rectifying state as will of course be understood by those skilled in the art.

Since the operation and arrangement of the embodiment shown in Fig. 2 is so similar in its fundamental aspects to the embodiment of Fig. 1, it is not believed necessary to trace in detail all of the individual circuits, similar reference numerals being used to identify similar parts in the two embodiments. In Fig. 2, the sensitive instrument means for controlling the tuning of the coil I3I and the means controlled by the relay 3 have been omitted in order to simplify the drawings, but it will of course be understood that the embodiment shown in Fig. 2 is intended for use with similar means. The cathodes or filaments H and 60 are shown in Fig. 2 as connected to the midpoints of the secondary windings of suitable filament heating transformers l0 and II, and it will of course be understood that similar heating means may be associated with the filaments of all of the embodiments of the invention herein shown, such heating means being omitted from Figs. 1 and Sin order to simplify the drawings.

In Fig. 2 a potentiometer, comprising a pair of fixed resistors 82 and 83 and an adjustable resistor 84, is connected across the source of supply representedby the supply conductors I39 and I40. The output circuit of the oscillator tube I34 extends from the positive source of supply I39 through the conductors 85 and 86, the right-hand portion of the resistor 84 and the adjustable terminal 81 of the potentiometer, the load impedance I33, the choke coil 50, the plate tank circuit including the inductance 52 and the condenser 53,

the plate 42, the filament H, theconductors con necting the filament to the heating transformer 10, and through the conductors 83 and 89 to the negative source of supply I40 which is connected to the left-hand fixed terminal of the potentiometer. The by-pass circuit for preventing the flow of radio frequency energy through the load impedance I33 and for providing suitable feed-back coupling to the input circuit of the tube I34, is similar to the embodiment shown in Fig. 1 in that it includes a coupling and blocking condenser 53. If desired, an additional inductance coil 90 may be included, as shown in Fig. 2, in the grid circuit between the tuning coil I3I and the filament 4|.

It is thought that the remaining circuits in the embodiment shown in Fig. 2 will be obvious without further description, in view of the description already given in connection with Fig. 1, and it will of course be understood that the potentiometer utilized in Fig. 2 is so adjusted that the voltage drop across the left-hand portion of the resistor 84 corresponds to the voltage supplied by the bias battery 64, the potentiometer I36 of Fig. 1 thereby compensating for a portion of the normal voltage drop across the load impedance I33 and applying a desired minimum negative potential to the grid 59 of the tube I32 when the oscillator tube I34 is in oscillatory condition.

Fig. 3 shows apparatus and circuit similar to that of Fig. 2 but arranged so that a thermo couple I corresponding to the thermo couple 22 of Fig. 1, an associated line resistor I42 and a sensitive instrument means or indicator meter I43 corresponding to the sensitive instrument means 2 of Fig. 1, are included in the feed-back circuit of the oscillator.

In control apparatus, such as being discussed, it is very important that in case of thermo couple breakage, the apparatus be turned to off position. If this is not done, the possibility of the furnace being left in the on" position is present, which might result in a furnace burn-out, which in commercial work is serious.

The circuit and apparatus of Fig. 3 is designed to obviate this condition of the furnace being left in on position in case of thermo couple breaka e.

Referring further to Fig. 3, since from the above explanation it will be understood that in the normal operating condition the plate current of the oscillator I34 is of low value, it follows that if the feed-back coupling circuit or oscillator return lead I44 from the coupling condenser I45, which corresponds to the coupling condenser 58 of Figs. 1 and 2, is open, the plate current will immediately rise, due to the cessation of oscillation.

This rise of the plate current flowing through the load impedance I33 will cause a drop in the plate current of the vacuum tube I32, as hereinbefore explained, with a consequent opening of the relay. This operation takes place if. the thermo couple I which is in series with the condenser I45 in the feed-back circuit burns out or opens, leaving closed the feed-back circuit through the resistance I42 and meter I43. Since the oscillator circuit constants are so chosen that a small increase in resistance in the oscillator return lead will cause the oscillator to go out of oscillation, protection from furnace burn-out due to thermo couple breakage is assured.

It will of course be understood that the thermo couple I4I of Fig. 3 corresponds to the thermo couple 32 of Fig. 1, and in actual operation would be subjected to the furnace temperature or the cator.

condition to be controlled so as to operate the sensitive instrument means I43, the pointer of which carries a metal flag (not shown) corresponding to the flag 6 on the pointer 4 of Fig. 1 for controlling the tuning coil I3I. In Fig. 3 no attempt has been made to show the instrument I48 in its proper relation to the coil I3I, since by positioning the instrument I43 as shown in Fig. 3 the illustration of the circuit connections is greatly simplified.

In Fig. 4 is shown a form of apparatus to insure protection from furnace bum-out, due to thermo couple breakage, wherein the protective apparatus is external to the oscillator circuits of the control apparatus. In this figure the apparatus shown includes a thermo couple I46, a pyrometric multiplier non-inductive resistor I41, with low temperature coefllcient, well known in the art, and an instrument indicator I48 which may be of the usual millivoltmeter type connected across the thermo couple. To this circuit is connected in proper polarity a battery I49 in series with a higher resistance I50. The pointer I 5| of the millivoltmeter may carry a flag which will cooperate with the pick-up coils of an oscillator circuit, such as previously described in connection with Figs. 1 and 2, to control the operation of a relay which controls the temperature of a furnace or the like with which the thermo couple is associated.

Normally, because of the very low resistance of the commercial thermo couple, the voltage drop across the thermocouple I46 from the battery resistor circuit is very low, very much smaller than can be discerned upon the scale of the indi- However, should the thermocouple I46 break or burn out, a large voltage is immediately occasioned across the thermocouple terminals, with an immediate throwing of the pointer of the millivoltrneter M8 to the top portion of the scale where it will be in juxtaposition to the pick-up coils of the oscillator control apparatus, such as previously described, causing a change in tuning of the oscillator and a consequent action of the relay controlled thereby to cause the furnace temperature to be reduced.

In Fig. 5 is shown a circuit arrangement which constitutes a preferred embodiment of my invention and in which a dual type of vacuum tube I52 is used, the method of operation being intended to simulate the action of a Thyratron tube of the self-rectified type, with alternating current grid voltage used for control without the necessity of the use of either the hot or cold cathode type grid control rectifier, which is commonly called the electron tube. With the circuit as shown, plate current changes take place between cut-off and saturation, without any intermediate plate current fixation. The operation of the circuit is as follows: One triode portion I53 of the dual type tube I52 is connected in a simple oscillator type circuit, consisting of plate tank I59, I and grid coil I58, with its associated grid leak and condenser I86 and I81. The grid coil I58 is so arranged as to be affected by the approachement of a flag such as previously described (not shown).

Alternating current voltages are obtained from a multi-winding transformer having a primary winding I connected to a suitable source of alternating current, as indicated, and having a plurality of secondary windings I66, I61, and I68 respectively arranged to supply suitable voltages to the tube circuits. Although my invention is not limited thereto and other suitable voltages may be employed, the secondary windings I66, I61, and I" in the embodiment illustrated are arranged to supply voltages of the magnitudes indicated in Fig. 5, i. e., 200 volts, 55 volts, and 185 volts respectively. For simplicity of description, these voltages will be considered as instantaneous values, the voltages across each of the secondary windings of the transformer being at all times in phase with each other, and since the tube sections I52 and I54 function as rectiflers the operation will be described only with respect to the positive half cycles of the alternating current voltages.

The output circuit of the oscillator tube section I53 may be traced from the left-hand or positive terminal of the secondary winding I66 through a radio frequency choke coil or inductance I68, the plate tank circuit I59, I60, the anode or plate I10, the cathode or filament IN, the conductors I12 and I18, the secondary winding I61, the voltage of which is in phase with the voltage of the winding I66, the conductor I14, the load impedance or resistor I62, and by way of the conductor I15 to the right-hand terminal of the secondary winding I66. A by-pass condenser I16 is connected, as shown, and in conjunction with the choke coil I69 prevents the flow of high frequency oscillatory currents through the transformer windings and through the load impedance I62. As will be apparent, the total voltage thus impressed across the load circuit of the tube section I53 in the embodiment shown, is the sum of the voltages of the secondary windings I 66 and I61, 1. e., 255 volts.

The output circuit for the repeater or amplifier tube section I 54 may be traced from the lefthand or positive terminal of the secondary winding I68 through the conductor I16a, the anode or plate I11, the cathode -or filament I18, the conductors I12 and I13, the secondary winding I61, the voltage of which is in phase with the voltage of the winding I68, the conductor I 14, the operating winding IGI of the relay, and by way of the conductor I19 to the left-hand terminal of the secondary winding I68. Thus a total voltage of 240 volts is impressed on the load circuit of the amplifier tube section. It will of course be understood that the relay winding I6I corresponds to the winding I35 oi the relay 3 in the embodiments shown in Figs. 1, 2, and 3, and

is arranged to control suitable apparatus such, for example, as the furnace shown in Fig. 1, in the manner hereinbefore described.

The grid bias for efiecting proper operation of therepeater tube section I54 is obtained in a manner similar to the hereinbefore described embodiments of the invention by connecting the grid or control electrode I80 to one end of the load resistor I62 through a conductor I8I, the remaining portion of this circuit extending from the filament I18 through the conductors I12 and I13, the secondary transformer winding I61, and the conductor I14 to the opposite end of the load resistor I62. It will be apparent that the voltage across the winding I61 is in opposi tion to and thus compensates for a portion of the voltage drop across the load impedance I62, and accordingly when the oscillator section I53 is in oscillatory condition so that a. plate current of low value flows through the load impedance I62, a minimum negative bias equal to the difference between the voltage of the winding I61, i. e. 55 volts and the voltage drop across the load impedance is impressed on the grid I80. The tube constants and the value of the load resistance are so prechosen as to provide a slightly negative grid bias under these conditions corresponding to the maximum-amplifier output current desired for proper operation or the relay.

An important feature oi. this embodiment of my invention resides in the connections for the input or grid circuit of the oscillator section I53, a regenerative coupling being provided between the grid I89 01 the oscillator section and the output circuit of the repeater section. As shown, the grid circuit for the oscillator tube section extends from the cathode or filament I" through the conductors I12 and I18, the transformer winding I61, the conductor I14, the relay winding I6I, a conductor I82, 8. radio frequency choke coil I83, conductors I84 and I85, the tuning coil I58, and by way of a suitable grid condenser and grid leak I 86 and I81 to the grid or input electrode I88. A suitable blocking or by-pass condenser I88 is connected between the filament III and the oscillator grid circuit as shown.

It will be apparent from the above-traced circuit that a fixed grid bias is applied to the grid I88 which is equal to the voltage drop across the relay winding I6I minus the voltage or the winding I61, and the resistance 0! the winding I8I is so chosen that with maximum current flowing in the output circuit or the amplifier tube section the maximum desired negative bias is applied to the grid I88 oi the oscillator section.

As heretofore explained in connection with Fig. 1, the plate tank circuit is tuned to resonance with the tuning coil in the oscillator grid circuit, with the metal flag in a position remote from the tuning coil, so that sustained oscillations are produced by the oscillator tube section. With the metallic flag in a remote position relative to the pick-up coil I58, the oscillator portion is in a normal state of oscillation with plate current or a low value, with the result that a low voltage drop exists across the load resistor I62 and a correspondingsmall bias is applied to the input circuit of the amplifier section I54, which positions its plate current rather high up on its grid voltage plate current graph. All conditions are in a state of stability.

Upon the fiag approaching the pick-up coil I58, the oscillator circuit is tie-tuned, causing its plate current to rise sharply, increasing the voltage drop across the resistor I62, which correspondingly increases the negative bias upon the amplifier section I54, with a consequent drop in its plate current through the relay I6I. The decrease in current through the relay IGI causes a decrease in the negative grid bias applied to the grid of the oscillation section I53, which tends to further increase the plate current of the oscillator section I53. This increase in the oscillator plate current further increases the voltage drop across the load resistor I62 and the negative bias upon the amplifier section I54 with the consequent effect of dropping the amplifier plate current to the cut-off point, .which causes zero level in plate current. When the flag recedes from the pick-up coil I58, the reverse occurs. The oscillator plate, current drops, decreasing the drop across resistor I62, which decreases the negative bias on the amplifier section I54; the plate current of the amplifier section tends to increase, increasing the drop across the relay I6I, which increases the negative bias on the grid of the oscillator I53, aiding in dropping the oscillator section plate current, which iurther tends to decrease the bias upon the amplifler section I54, etc., with the result that the final positioning of the plate current of amplifier section I54 isat saturation. By the Judicious choosing 01' load resistance I62, oi the resistance of the relay winding I6I and the proper apportioning of bias voltages as shown, the limits or plate current between cut-ofi and saturation may be fixed at any desired value. The

,result is that control of .this plate current change is always maintained with the obtaining oi abrupt plate current changes of a very rapid nature. The result obtainable is comparable to the triggering ofi of a 'I'hyratron" type hot cathode grid control rectifier without the necessity of using gas-filled tubes.

It is not necessary that the apparatus be limited to the use of a dual purpose vacuum tube, containing double triode elements, since this type of tube has been only chosen as a matter of convenience. Separate triode elements may be operated in the same manner with either alternating current or direct current voltages applied, the use of the self-rectified circuit being only a matter of choice or convenience as is readily apparent.

In summary, the advantages of this circuit are manifest, inasmuch as a relay with a high throw-out percentage is not necessary, since the plate current changes through said relay are very rapid and very large. It is impossible to lose control of the oscillator, since, because of the fact that it is self-rectified, oscillations, no matter how minute, will always reoccur. Other variations of this circuit will readily occur to those versed in the art, such as the use of a.

common power supply, with a self-rectified circuit, instead of separate voltages as shown. Such circuits have been designed and are entirely feasible, the one shown being one of a family of such circuits and being chosen as the most descriptive of the above-explained operation.

Further modifications will be apparent to those skilled in the art and it is desired, there fore, that the invention be limited only by the prior art and the scope of the appended claims.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

1. In a control system, the combination of a vacuum tube oscillator having input and output circuits, a load impedance effectively included in said output circuit, a vacuum tube repeater having an input circuit coupled to said load impedance to control the output circuit of said re-' peater in accordance with changes in the voltage drop across said load impedance, an electroresponsive device having an operating winding effectively included in said repeater output circult, and means responsive to a condition to be controlled by said electro-responsive device for aiiecting the tuning of said oscillator circuit to vary the voltage across said load impedance whereupon said repeater causes operation of said electro-responsive device.

2. In a control system, the combination of a vacuum tube oscillator having tuned input and output circuits, a load impedance eilectively included in said output circuit adapted to be traversed only by the nonpulsating component of the current in said output circuit, a vacuum tube repeater having an input circuit coupled to said load impedance for energization in ac-. cordance with the voltage drop across said impedance, a repeater output circuit, a relay having an operating windingconnected in said repeater output circuit, and means responsive to a condition controlled by operation oi said relay including a part movable toward and away from a portion of said oscillator input circuit to change the tuning of said oscillator, whereby the voltage drop across said load impedance is varied to effect operation of said relay.

3. In a control system, the combination of an oscilleor circuit including input and output circuits coupled with the input and output electrodes of an electron discharge device, means including a variable position control element responsive to a condition to be controlled, said element being movable with respect to a portion of said oscillator circuit to change the tuning thereof, a load impedance eifectively included in said output circuit so as to be traversed only by the non-impulsing component of the output current, an amplifier circuit including input and output circuits coupled with th input and output electrodes of a second electron discharge device, said amplifier input circuit being so coupled with said load impedance as to vary the amplifier output current in accordance with changes in the voltage across said load impedance, and an electroresponsive device controlled by said amplifier output current for controlling said condition upon movement of said variable position control element.

4. In a control system, an electron discharge tube comprising two sections each including input and output electrodes, a tuned input circuit coupled between the input electrodes of one of said sections, a tuned output circuit coupled between the output electrodes of said one section, said tuned circuits being so coupled as to provide for operation of said one section as an oscillator,

an input circuit coupled between the input electrodes of the other of said sections, an output circuit coupled between the output electrodes of said other section, said last mentioned input and out put circuits providing for operation or" said other section as a repeater, impedance means common to said oscillator output circuit and said repeater input circuit for causing variations in the cur" rent flow in said repeater output circuit upon changes in the tuning of said oscillator section, means movable with respect to a portion of one of said circuits of said oscillator section to change the tuning thereof, and relay means responsive to the consequent changes in the output current of said repeater section.

5. In a control system, an electron discharge tube comprising two sections each including input and output electrodes, a tuned input circuit coupled between the input electrodes of one of said sections, a tuned output circuit coupled between the output electrodes of said one section, said tuned circuits being so coupled as to provide for operation of said one section as an oscillator, an input circuit coupled between the input electrodes of the other of said sections, an output circuit coupled between the output electrodes of said other section, said last mentioned input and output circuits providing for operation of said other section as a repeater, impedance means common to said oscillator output circuit and said repeater input circuit for causing variations in the current flow in said repeater output' circuit upon changes in the tuning of said oscillator section, an electro-responsive device having an operating winding effectively included in said repeater output circuit for operating said device in response to predetermined changes in the output current, and means responsive to changes in a condition controlled by said electro-responsive device including a variable position part movable with respect to a portion of one of said oscillator circuits for changing the tuning thereof and causing operation of said electro-responsive device.

6. In a control system, the combination of a vacuum tube oscillator having tuned input and output circuits, a load impedance eflectively included in said output circuit, a vacuum tube repeater having an input circuit coupled for energization in accordance with the voltage across said load impedance, an output circuit for said repeater, an electro-responsive device having a winding eiIectively included in said repeater output circuit, means movable with respect to a portion of said oscillator for afiecting the tuning thereof to vary the current flowing in said oscillator output circuit and said load impedance whereby the input circuit of said repeater is infiuenced to cause a change in the energization of said winding, and a coupling between said winding and said oscillator input circuit for causing a cumulative change in the output of said oscillator in response to said change in the energization of said winding so as further to change the energization of said winding, whereby minute movements of said means to vary the tuning of said oscillator effect sharp variations in the output current or said repeater between cut-on and saturation quickly to operate said electro-responsive device.

7. In a control system, the combination of a vacuum tube oscillator having tuned input and output circuits, 9. load impedance effectively included in said output circuit, a vacuum tube repeater having an input circuit coupled for energization in accordance with the voltage across said load impedance, an output circuit for said repeater, an electro-responsive device having a winding effectively included in said repeater output circuit, means movable with respect to a portion of said oscillator for aiiecting the tuning thereof to vary the current flowing in said oscillator output circuit and said load impedance whereby the input circuit of said repeater is influenced to cause a change in the energization of said winding, and means coupling said winding with said oscillator input circuit so proportioned and arranged that changes in the energization of said winding are reflected through said oscillator and repeater to cause further changes in the energization of said winding in a cumulative sense, whereby a change in the tuning of said oscillator of sufiicient magnitude to effect a change in th output current of said repeater causes a sharp variation of said output current between cut-01f and saturation quickly to operate said electro-responsive device.

8. In a control system, the combination of a vacuum tube oscillator having tuned input and output circuits, a load impedance efiectively included in said output circuit, a vacuum tube repeater having an input circuit coupled for energization in accordance with the voltage across said load impedance, an output circuit for said repeater, an electro-responsive device having a winding effectively included in said repeater output circuit, means movable with respect to a portion of said oscillator for afiecting the tuning thereof to vary the current flowing in said oscillator output circuit and said load impedance whereby "the input circuit of said repeater is influenced to cause a change in the energization of said winding, and a regenerative coupling between said winding and said oscillator input circuit for effecting a sharp variation of the repeator output current between saturation and cutoff in response to a change inthe tuning of said oscillator independently of the magnitude of said change and the degree of movement of said movable means.

9. In a control system, the combination of an oscillator circuit including input and output circuits coupled with the input and output electrodes of an electron discharge device, a variable position control element responsive to a condition to be controlled and movable with respect to a portion of said oscillator circuit to change the tuning thereof, an amplifier circuit including input and output circuits coupled with the input and output electrodes of a second electron discharge device, means coupling said amplifier input circuit with said oscillator output circuit whereby a change in the tuning of said oscillator circuit effects a change in the output current of said amplifier, an electro-responsive device having an operating winding adapted to operate said device between two positions upon changes of predetermined magnitude in said amplifier output current, and a regenerative coupling between said winding in said amplifier output circuit and said oscillator input circuit for efiecting a sharp variation of said amplifier output current between cut-off and saturation in response to an initial change in the tuning of said oscillator of sufllcient magnitude to effect a slight change in said amplifier output current, whereby said electroresponsive device is quickly operated between said two positions in response to a critical movement of said control element regardless of the magnitude or speed of said movement.

10. In a control system, an electron discharge tube comprising two sections each including input and output electrodes, at tuned input circuit coupled between the input electrodes of one of said sections, a tuned output circuit coupled between the output electrodes of said one section, said tuned circuits being so coupled as to provide for operation of said one section as an oscillator, an input circuit coupled between the input electrodes of the other of said sections, an output circuit coupled between the output electrodes of said other section, said last mentioned input and output circuits providing for operation of said other section as a repeater, impedance means common to said oscillator output circuit and said repeater input circuit for causing variations in the current fiow in said repeater output circuit upon changes in the tuning of said oscillator section, means movable with respect to a portion of one of said circuits of said oscillator section to change the tuning thereof, relay means responsive to predetermined changes in the output current of said repeater section, and a regenerative coupling between said repeater output circuit and said oscillator input circuit for efiecting a sharp variation of said repeater output current upon a slight change in the tuning of said oscillator section quickly to operate said relay means independently of the magnitude of said change in tuning.-

ll. In a temperature control system, the combination with an electro-responsive device for controlling the temperature source and temperature responsive means affected by the temperature of said source, of a vacuum tube oscillator having input and output circuits at least one of which is tuned to provide sustained oscillations, said output circuit being effectively coupled to said electro-responsive device to control the operation thereof, a variable position part connected tor operation by said temperature responsive means, said part being movable to effect the tuning; of said oscillator, and means for controlling said oscillator to effect operation of said. electroresponsive device upon interruption of said connection between said temperature responsive means and said variable position part.

12. In a temperature control system, the combination with a relay for controlling the temper- 10 ature source. and a thermocouple circuit affected by the temperature of said source, of a vacuum tube oscillator having tuned input and output circuits, means for eifecting operation of said relay in response to changes in the current in IG said output circuit, an instrument having a variable position part controlled by said thermocouple circuit, said variable position part being arranged upon movement thereof to affect the tuning of said oscillator input circuit whereby 20 operation of said relay is accomplished, and means for effecting operation of said relay upon interruption of said thermocouple circuit.

13. In a temperature control system, the combination with a relay for controlling the tem- 35 perature source and a thermocouple circuit affected by the temperature of said source, of a vacuum tube oscillator having tuned input and output circuits, means for effecting operation of said relay in response to changes in the current in said output circuit, an instrument having a variable position part controlled by said thermocouple circuit, said variable position part being arranged upon movement thereof to affect the tuning of said oscillator input circuit whereby operation of said relay is accomplished, and means for effecting a change in the tuning of said oscillator upon interruption of said thermocouple circuit to cause operation of said relay.

' 14. In a temperature wntrol system, the com-' o bination with a relay for controlling the tem-- perature source and a thermocouple circuit affected by the temperature of said source, of a vacuum tube oscillator having tuned input and output circuits, means for efiecting operation of said relay-in response to changes in the, current in said output circuit, an instrument having a variable position part controlled by said thermocouple circuit, said variable position part being arranged upon movement thereof to aifect the tuning of said oscillator input circuit 'whereby operation of said relay is accomplished, and means efifectively coupling said thermocouple circuit with said oscillator input circuit to effect a change in the current flowing in the said oscillator output circuit upon interruption of said thermocouple circuit thereby to cause operation of said relay.

15. In a temperature control system, the combination with a relay for controlling the temm perature source and a thermocouple circuit affected by the temperature of said source, of a vacuum tube oscillator having tuned input and output circuits, means for effecting operation of said relay in response to changes in the current 5 in said output circuit, an instrument having a variable position part controlled by said thermocouple circuit, said variable position part being arranged upon movement thereof to affect the tuning of said oscillator input circuit whereby 7o operation of said relay is accomplished, and means for effecting movement of said variable position part upon interruption of said thermocouple circuit to change the tuning of said oscillator and cause operation of said relay.

16. In combination, an electron discharge tube having input and output circuits adapted to be tuned to resonance to cause said tube to operate as an oscillator, a load impedance effectively included in said output circuit so as to be traversed only by the non-pulsating component of the oscillator output current, whereby the voltage drop across said impedance increases when the oscillatory condition of said tube varies from resonance, a repeater tube having input and output circuits, a source or" biasing potential, and means connecting said load impedance and said source in series relation in said repeater input circuit with the voltage of said source in opposition to and of less magnitude than said voltage drop when said oscillator is in resonant condition, whereby the resulting bias voltage impressed on said repeater input circuit is a desired minimum during resonant conditions and increases to a desired maximum upon the cessation of oscillations to control the output of said repeater tube.

1?. In combination, a vacuum tube oscillator having tuned input and output circuits, a load impedance en'ectively included in said output circuit, a vacuum tube repeater having an input circuit coupled for energization in accordance with the voltage across said load impedance, whereby changes in the tuning of said oscillator are efiective to control said repeater, an output circuit for said repeater, and means coupling said output circuit of said repeater with said input circuit of said oscillator so proportioned and arranged that changes in the output of said repeater tube are reflected through said oscillator and repeater to cause further changes in the output of said repeater in a cumulative sense, whereby a change in the tuning of said oscillator of suiflcient magntitude to effect an initial change in the output of said repeater causes a sharp variation of said repeater output between cut-oil and saturation.

18. In combination, a vacuum tube oscillator having tuned input and output circuits, a load impedance effectively included in said output circuit, a, vacuum tube repeater having an input circuit coupled for energization in accordance with the voltage across said load impedance, whereby changes in the tuning of said oscillator are efiective to control said repeater, an output circuit for said repeater, and a regenerative coupling between said repeater output circuit and said oscillator input circuit for effecting a sharp variation of the repeater output current between saturation and cut-off in response to a change in the tuning of said oscillator independently of the magnitude of said change.

19. In combination, an electron discharge tube having tuned input and output circuits coupled for the generation of sustained oscillations upon proper tuning thereof, a load impedance effectively included in said output circuit so as to be traversed, only by the non-pulsating component of the current in said output circuit whereby the voltage drop across said impedance varies with variations in the tuning of said circuits, a repeater tube having input and output circuits, 8. source of biasing potential, means connecting said load impedance and said source in series relation in said repeater input circuit with the voltage of said source in opposition to and of less magnitude than said voltage drop when said tuned circuits are in resonance, whereby a desired minimum bias is impressed on said repeater input a circuit which increases with changes in the tuning of said tuned circuits, and a regenerative coupling between said repeater output circuit and said tuned input circuit for varying in a cumulative sense the energization of said tuned input circuit upon a change in tuning of said tuned circuits of suflicient magnitude to effect a change in the repeater output current, whereby a sharp variation of said repeater output current between saturation and cut-off without intermediate fixation is caused by a slight change in the tuning of said tuned circuits.

20. In a temperature control system, the combination with an electro-responsive device for controlling a temperature source and temperature-responsive means affected by the temperature of said source, of a vacuum tube oscillator having input and output circuits tuned to provide sustained oscillations, a load impedance eflectively included in said output circuit for traversal only by the non-pulsating component of the oscillator output current whereby the voltage drop across said impedance increases when the oscillatory condition of said tube varies from resonance, a repeater tube having input and output circuits, a source of bias potential, means connecting said load impedance and said source in series relation in said repeater input circuit with the voltage of said source in opposition to and of less magnitude than said voltage drop when said oscillator is in resonant condition, whereby the resulting bias voltage impressed on said repeater input circuit is a desired minimum during resonant conditions, said electro-responslve device being eifectively coupled in the output circuit of said repeater tube for operation in response to variations in the repeater output current, a variable position part connected for operation by said temperature-responsive means, said part being movable to control the tuning of said oscillator and thereby increase to a desired maximum the voltage drop across said impedance and the bias voltage impressed on said repeater input circuit upon the cessation of oscillations, whereby operation of said electro-responsive device is effooted, and means for so controlling said oscillator as to eiIect operation of said electro-responsive device upon interruption oi said connection between said temperature-responsive means and said variable position part.

21. In a control system, the combination of an electron discharge tube having input and output circuits adapted to be tuned to resonance to cause said tube to operate as an oscillator, a load impedance effectively included in said output circuit so as to be traversed only by the nonpulsating component of the oscillator output current, whereby the voltage drop across said impedance increases when the oscillatory condition of said tube varies, from resonance, a repeater tube having input and output circuits, an elec tro-responsive device having an operating winding effectively included in said repeater output circuit, a, source 01 biasing potential, means connecting said load impedance and said source in series relation in said repeater input circuit with the voltage of said source in opposition to and of less magnitude than said voltage drop when said oscillator is in resonant condition, and means responsive to a condition to be controlled by said electro-responsive device for varying the tuning of said oscillator from said resonant condition, whereby the resulting bias voltage impressed on said repeater input circuit is a desired minimum during resonant conditions and increases to a desired maximum when operation of said condition-responsive means to cause a cessation of oscillations, said increase in the resulting bias voltage being effective to control the output of said repeater tube and cause operation of said electro-responsive device.

22. In a temperature control system, the combination of an electron discharge tube having input and output circuits adapted to be tuned to resonance to cause said tube to operate as an oscillator, a load impedance effectively included in said output circuit 'so as to be traversed only by a non-pulsating component of the oscillator output current, whereby the voltage drop across said impedance increases when the oscillatory condition of said tube varies from resonance, a repeater tube having input and-output circuits, a source of biasing potential, means connecting said load impedance and said source in series relation to said repeater input circuit with the voltage of said source in opposition to and of less magnitude than said voltage drop when said oscillator is in resonant condition, an electro-responsive device having an operating winding ef- Iectively included in said repeater output circuit for controlling a source of temperature in response to variations in the energization of said winding, and temperature-responsive means afiected by the temperature of said source including a variable position part movable to control the tuning of said oscillator circuit, whereby the bias voltage impressed on said repeater input circuit varies from a desired minimum during resonant conditions to a desired maximum upon movement of said variable position part to cause a cessation of oscillations, said variation in the bias voltage controlling the output of said repeater tube to operate said electro-responsive device in accordance with a change in the temperature of said source.

23. In combination, an electron discharge tube comprising two sections each including input and output electrodes, 9. tuned input circuit coupled between the input electrodes of one of said sections, a tuned output circuit coupled between the output electrodes of said one section, said tuned circuits being so coupled as to provide for operation 01 said one section as an oscillator, a load impedance efl'ectively included in said output circuit so as to be traversed only by a non-pulsating component of the oscillator output current, whereby the voltage drop across said impedance increases when the oscillatory condition of said tube varies from resonance, an input circuit coupled between the input electrodes of the other of.

said sections, an output circuit coupled between the output electrodes of said other section, the last-mentioned input and output circuits providing for operation of said other section as a repeater, a source of biasing potential, and means connecting said load impedance and said source in series relation in said repeater input circuit with the voltage of said source in opposition to and of less magnitude than the said voltage drop when said'oscillator section is in resonant condition, whereby the resulting bias voltage impressed on said repeater input circuit is a desired minimum during resonant conditions and increases to a desired maximum upon the cessation of oscillations to control the output of said THEODORE A. COHEN. 

